Microbes bioassay using

One of the most important quality characteristics of advanced oxidation processes is their ability to reduce the toxicity of an industrial wastewater and to enhance its biodegradability (see Chapter 7.1.5). This criterion can be established by several standardized procedures using different test organisms ranging from microbes to intact animals (cf Tab. 5-1). An easy to perform variant is the bioluminescence assay that uses the inhibition of the bioluminescence intensity of the test organism Vibrio fischeri in the presence of toxic substrates. This is a bioassay used worldwide for the evaluation of toxicity data of individual chemicals or of industrial wastewaters (Froehner et al, 2000, DIN, 1991). Commercial systems are... 

In this review we point out the value of bioassays in the study of allelopathic interactions but do not attempt to critically evaluate or prioritize bioassay techniques that have been published. Since it is also not possible to propose a general bioassay for researchers, we present selected examples of bioassays that have been used to understand these plant-plant and plant-microbe chemical interactions. Furthermore, we attempt to provide an overview of some bioassays that are useful or that may be adaptable to allelochemicals. The general focus will be on laboratory bioassays since they are paramount to determine quantitative effects of allelochemicals and to ascertain actual mechanisms of allelopathy in nature. 

Many new microbial compounds with potential blocherbicldal activity have been Isolated, chemically characterized, and a portion of their biological activities determined using various bioassay techniques or by direct plant screening. Some of these compounds are virulence factors of plant pathogens, thus Information on these phytotoxins can benefit the development of microbes as herbicides and potentially provide new chemical herbicides. Data on some of these compounds and their structures are presented. Information on source, biological activity, and possible mode of action (when available) Is briefly summarized. 

Many other phytotoxins not presented here have been structurally characterized and tested In some plant bioassay systems. Numerous other reported phytotoxin studies are In the "active fraction" stage and structure elucidation of the active components has not been achieved. Nevertheless, from the data presented. It can generally be concluded that diverse microbes produce a broad range of chemistries with phytotoxic activities chemical and biochemical synthesis of almost all of these compounds Is unknown (but derivitizatlon studies to alter phytotoxic activity have been used In a few Instances) knowledge of the spectrum of species susceptible to these compounds Is Incomplete (many weed and crop species have not been tested some compounds are toxic to organisms other than plants) and the molecular mode of phytotoxin action Is unstudied or unknown for most. The major exception Is the vast amount of data on blalaphos, phosalacine, and phosphinothricin, which have achieved commercial status. 

These same data profiles have been generated for all of the microbes grown to date. As each microbial extract is fractionated, the appropriate bioassay is used to guide which fractions are resolved into pure compounds and eventually characterized. Three such studies will be described below. 

A feasibility study on the potential use of a luminescent bacteria bioassay in the toxicity screening oftrichothecenes is presented. The toxic effects of four 12,13-epoxytrichothecenes to bioluminescent bacteria were determined for the first time using the Microtox " Toxicity Analyzer (TM Trademark of Microbics Corporation, Carlsbad, California). The influence of test temperature and exposure time on the toxic effect oftrichothecenes to the luminescent bacteria are discussed. The toxicities measured are compared with toxic effects determined using other bioassays. Potential relationships between the toxicities found and variations in the chemical structure of these compounds are considered. 

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